Lower back pain is commonly caused by deterioration of intervertebral discs and facet joints, resulting in stenosis of intervertebral foramina and thus causing pressure on spinal nerve roots where they exit from the spinal nerve canal and extend laterally away from the spine through the intervertebral foramina. As people age, intervertebral discs and other parts of the spinal column deteriorate. Discs may shrink, allowing vertebrae to approach one another more closely, and facet joints may develop bone spurs, protruding into the foramina and reducing the available space through which nerve roots must extend. Pressure on nerve roots due to facet arthrosis, ligamentum flavum infolding, and disc herniations often results and can cause severe and even debilitating pain. Degeneration of discs may also allow a vertebra to become misaligned with respect to an adjacent vertebra, resulting in spondylolisthesis.
It is well known to decompress the spine, that is, to relieve pressure on the spinal exiting and traversing nerves by performing bilateral laminotomies and to immobilize adjacent vertebrae with respect to each other. Installing pedicle screws and rods can also be used to stabilize the spine if necessary.
It is also known that facet joints can be immobilized, and that a lumbar vertebra can be fused together with an adjacent lumbar vertebra to prevent the vertebrae from moving relative to each other, in order to prevent future impingement on spinal nerves between the fused vertebrae. In the past, however, vertebral fusion has typically been accomplished by the use of pedicle screws and rods to immobilize vertebrae relative to each other. Compared with facet fixation, pedicle screws and rod insertions requires a longer operative time, and results in increased blood loss, and increased paraspinal muscle trauma. Since spinal deterioration of the sort which requires such surgical remedy usually occurs in older patients, it would be desirable to be able to immobilize and fuse vertebrae in a procedure that takes less time, less anesthesia, less blood loss, and less soft tissue trauma.
Recently, less invasive procedures have been utilized, such as percutaneous installation of screws into facet joints to immobilize them, as disclosed, for example, in Serhan et al. U.S. Patent Application Publication Document No. US2005/0149030-A1. It is also known to insert a long screw through a spinous process and into a facet joint, as shown in Obenchain et al. U.S. Patent Application Publication Document No. US2004/0254575-A1.
Many different methods and devices are known for use in immobilizing vertebrae relative to one another to promote fusion. One type of device intended for immobilizing adjacent lumbar vertebrae with respect to each other includes a spinous process fixation system in which a clamp is fastened to the spinous processes of two adjacent vertebrae, fastening them together. Such devices are disclosed in Chin et al. U.S. Patent Application Publication Document No. US2007/0270840-A1 and Lamborne et al. U.S. Patent Application Publication Document No. US2008/0183211-A1. Such clamps can be attached so as to distract the vertebrae from each other, but because of the location of such a clamp, spaced apart dorsally from the deteriorated intervertebral discs, use of such a clamp may result in reduced lordosis, thereby resulting in additional strain experienced by joints between other vertebrae. Such clamp devices, moreover, often cannot be used in an L5-S1 location, because of the lack of a large enough spinous process on the sacrum. Additionally, the interconnected spinous processes may fail under the forces applied through such clamps.
What is desired, then, is a device and a method for its use in relieving pressure on spinal nerves and in fusing vertebrae together, using a minimally invasive procedure that can be performed in a significantly shorter time than has previously been required for vertebral fusion procedures such as those including the installation of pedicle screws and rods.